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HE-500, LCD2, D5000, DT770, SR80, on a speaker amp (Emotiva mini-X A-100) Project - Page 196

post #2926 of 3613
Quote:
Originally Posted by Drsparis View Post
 

Merry Christmas to all!

 

I will be building a little resistor box for this and my Millenia MG3 amp. I have been playing around with Robrob's resistor calculator and had a quick question. Using 7/1 ohm resistors instead of 6/2 seem to have a lower headphone output impedance and also a effective speaker load closer to 8. apart from 18db of atenuation compared to 12.5 would this not be better? I dont understand half of what im saying so please feel free to correct me or give me any insight! 

 

I have read that some people have notticed lower dynamics with these boxes, has anyone found a sweetspot? I guess this is the 6/2 combo...?

It just depends on how much attenuation you need. If the noise floor hiss is very noticeable or you have very little useable volume knob then 12dB or may be needed. But too much attenuation may have a negative effect on sound quality (still not sure about this though).

post #2927 of 3613
Quote:
Originally Posted by Armaegis View Post
 

 

I think it's a really bad idea that switch is even there in the first place. Attaching a balanced (or fully differential, whatever you want to call it) amp to that box is just a recipe for disaster. An accidental bump of the switch or someone who doesn't fully understand, and boom you're gonna let the magic smoke out.

 

 

I'm using a latching toggle switch on the Robinette Box so you'll have to make a concerted effort to change the amplifier mode switch. When connecting the box to an amp you will have to ensure the switch is set correctly before powering up the amp, but if you have problems with that sort of thing you probably wouldn't be able to build a Robinette Box anyway.

 

If you don't like the idea of using resistors to protect a balanced amp from single-ended headphones' common ground you can go with version 2 of the box which doesn't offer that function.

 

As far as how the resistors will affect the sound quality it depends on the amp and headphones used.

 

Rob

post #2928 of 3613

A switch to bypass the L-pad is fine. That sort of thing has been around for decades. It's the switch up top that's the danger. Version 2 still has the potential to short the negative terminals of a balanced amp and blow up your amp and/or damage your headphones.

 

A single ended amp should have a single ended adapter. A balanced amp should have a balanced adapter. The two should never meet*, lest accidents occur. A more robust single ended adapter would have the sleeve connected to only one negative post since it wouldn't matter, and on the off chance someone used it on a balanced amp it will sound strange, but it shouldn't cause any immediate problems. 

 

Tying the grounds together with resistors in a single ended adapter makes no sense whatsoever. With a single ended amp, there's no need and all you're doing is killing the damping factor. Just drop one leg of the negatives and be done with it. On a balanced amp, yeah sure the resistors will protect the amp from shorting... but that floating point between the negatives isn't even a proper ground. You're just creating a (sort of) mono signal from the two negatives and connecting that across your left and right, which is just going to give you a mess of sound.

 

Take your V3 schematic, drop the "amp mode switch" entirely, and run just one negative from the 4-pin XLR to the sleeve of the TRS jack. It's a significantly safer design, and worst case scenario someone plugs their single-ended headphone into a balanced amp and it just sounds funny.

 

 

*ok you can connect a balanced adapter to a single ended amp because all 4 wires are kept separate and ideally none will ever meet without a load in between


Edited by Armaegis - 12/26/13 at 11:12am
post #2929 of 3613
Quote:
 Take your V3 schematic, drop the "amp mode switch" entirely, and run just one negative from the 4-pin XLR to the sleeve of the TRS jack. It's a significantly safer design, and worst case scenario someone plugs their single-ended headphone into a balanced amp and it just sounds funny.

Naah.

 

If I was designing a commercial product I'd add more safeguards. But I'm not.

post #2930 of 3613

:D  You 2.  It's holiday season.  Share some love...

post #2931 of 3613
Quote:
Originally Posted by robrob View Post
 

Naah.

 

If I was designing a commercial product I'd add more safeguards. But I'm not.

 

I see. So you're just going to continue deliberately promoting an unsafe design to the head-fi community.

 

It's not even "adding" a safeguard (which you can do with two diodes, but I digress). Take out the bad part that's an actual danger. Someone's going to build that "RobinetteBox" of yours and wind up burning out their amp, damaging their headphones, or possibly start a fire.


Edited by Armaegis - 12/26/13 at 2:23pm
post #2932 of 3613
So I'll do like you suggest, armaegis. Not going to use unbalanced headphones with a balanced amp, then, at least for now. Thank you!
post #2933 of 3613

Had the emo go past 2 o'clock today with my speakers. I was almost afraid bad things were to happen, hehe.

post #2934 of 3613
Quote:
Originally Posted by davidsh View Post
 

Had the emo go past 2 o'clock today with my speakers. I was almost afraid bad things were to happen, hehe.


LOL I took it to about 3 or 4 o'clock with my cousin's magnepan 1.6's! :)

post #2935 of 3613
Quote:
Originally Posted by Nimzerz View Post
 
Quote:
Originally Posted by davidsh View Post
 

Had the emo go past 2 o'clock today with my speakers. I was almost afraid bad things were to happen, hehe.


LOL I took it to about 3 or 4 o'clock with my cousin's magnepan 1.6's! :)

Wow, you are brave! No clipping or anything? My speakers are also only 8 ohms. Those mangepans are pretty darn insensitive. 83 dB/W if I am not mistaken. Mine are like 90 db/W.

 

Didn't the amp get warm or something?


Edited by davidsh - 12/26/13 at 6:54pm
post #2936 of 3613
Quote:
Originally Posted by davidsh View Post
 

Wow, you are brave! No clipping or anything? My speakers are also only 8 ohms.


I don't believe there was any clipping till it hit 4 o'clock (which might've also been distortion and whatnot from the song, who knows?). This amp really does deliver TRUE power! At the point of clipping its louder than practical listening so...no problem haha

 

We ran the amp at i think 2 or 3 o'clock and it only got warm (we kept it running for maybe 10min). But it was also sitting on top of his Harmon Kardon receiver which gets super fricken hot even when it's not running... So in other words, it barely warmed up


Edited by Nimzerz - 12/26/13 at 7:04pm
post #2937 of 3613
Quote:
Originally Posted by Nimzerz View Post
 
Quote:
Originally Posted by davidsh View Post
 

Wow, you are brave! No clipping or anything? My speakers are also only 8 ohms.


I don't believe there was any clipping till it hit 4 o'clock. This amp really does deliver TRUE power! At the point of clipping its louder than practical listening so...no problem haha

Hehe, nice. I must try to see how much I can push it be4 clipping occurs. If I dare. It'll be pretty loud, would require peaks past 107 dB. Edited my post from before by the way.

post #2938 of 3613
Quote:
 It's not even "adding" a safeguard (which you can do with two diodes, but I digress). Take out the bad part that's an actual danger. Someone's going to build that "RobinetteBox" of yours and wind up burning out their amp, damaging their headphones, or possibly start a fire.

You left off the part about burning down the house and all of London.

 

A couple of reverse current blocking diodes is a good idea. Why didn't you suggest it earlier? (that's a rhetorical question, I know why ;))

 

Like I said, if you can build one of my interfaces you can set the switch when moving it to a new amp. That's the only time that switch needs to be moved and the latching toggle will keep it from being moved accidentally.


Edited by robrob - 12/27/13 at 4:42am
post #2939 of 3613

Armaegis, after thinking about the reverse current blocking diodes I realized we're working with an AC audio signal. Wouldn't reverse current blocking diodes act as half-wave rectifiers and remove the negative voltage half of the audio signal?

post #2940 of 3613
Quote:
Originally Posted by robrob View Post
 

Armaegis, after thinking about the reverse current blocking diodes I realized we're working with an AC audio signal. Wouldn't reverse current blocking diodes act as half-wave rectifiers and remove the negative voltage half of the audio signal?

Should there be any negative voltage signal unless we are talking balanced? 

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